1. Field of the invention
This invention relates generally to a frequency multiplier for providing an output signal having a frequency greater than that of the frequency of the input signal, and more particularly to a direct digital frequency multiplier that multiplies frequencies by a predetermined factor.
2. Background of the invention
A frequency multiplier generates an output signal whose frequency is a multiple of the frequency of the input signal. Frequency multiplier circuits have a wide variety of uses, especially in generating high frequency signals. In electronics, for example, the manipulation of frequencies in the audio and radio frequency spectrum is often useful.
High frequency signals are more unstable and generate more interference than low frequency signals. Interference from the movement of high frequency signals is a most noticeable problem in integrated circuits, so much so that the function of the integrated circuit may be adversely affected. Therefore, it is advantageous to transmit low frequency signals across integrated circuits, and then to convert low frequencies to high frequencies only where needed. Reducing the presence of high frequency signals in an integrated circuit will lower the level of electromagnetic interference and likely reduce errors due to such interference.
Conventional frequency multiplier systems employ digital, analog, or a combination of both technologies. For example, in an analog frequency multiplier, an input signal is applied to a non-linear device that produces at its output a wide range of signals in a frequency spectrum whose components are integer multiples of the input frequency. A filter of predetermined center frequency is then positioned at the output of the non-linear device to select the desired frequency in the output signal frequency range.
Analog systems, however, are often less accurate than their digital counterparts. For example, analog frequency multipliers suffer from an inability to quickly and accurately respond to changes in input frequency and further, due to their inherent temperature sensitivity, may give poor performance when the temperature of the system is subject to change. Further, analog systems do not easily lend themselves to incorporation into LSI/MSI arrays.
U.S. Pat. No. 4,063,070 discloses a prior art frequency multiplier. However, the design disclosed therein has a slower response time since frequency changes require a full cycle interval. In addition, the function of this known multiplier can be improved.